1. Field of the Invention
The present invention relates to a golf ball and a process for preparing the same, more particularly to improving abrasion-resistance, durability and resilience of the golf ball having a cover containing a urethane resin as a base resin.
2. Description of the Related Art
As a base resin which constitutes a cover of a golf ball, ionomer resin and polyurethane are used. The cover using the ionomer resin is widely used for its excellent resilience, durability and workability, but because of its high rigidity and hardness, problems such as bad shot feeling, inadequate spin performance and inferior controllability are pointed out. On the other hand, polyurethane is used as a base resin which constitutes the cover because it provides an improved shot feeling and spin property compared with ionomer resin. For example, Japanese unexamined patent publication No. S51-74726, Japanese patent No. 2,662,909, and U.S. Pat. No. 4,123,061 disclose a use of thermosetting polyurethane, while U.S. Pat. No. 3,395,109 and U.S. Pat. No. 4,248,432 disclose a use of thermoplastic polyurethane for a cover. A use of the thermosetting polyurethane as a cover material can provide a golf ball with excellent abrasion-resistance, but the process of preparing the golf ball becomes complicated. Further, a golf ball using thermoplastic polyurethane as a cover material has inadequate abrasion-resistance, shot feeling and resilience, compared with a golf ball using thermosetting polyurethane.
Japanese unexamined patent publication No. H11-178,949 and Japanese unexamined patent publication No. 2,002-336,379, for example, disclose an improvement of the abrasion-resistance of a cover which uses thermoplastic polyurethane. Japanese unexamined patent publication No. H11-178,949 discloses a solid golf ball having a solid core and a cover covering the solid core wherein a resin component constituting the cover contains a reaction product between a thermoplastic polyurethane elastomer and a blocked isocyanate as a main component. Further, Japanese unexamined patent publication No. 2,002-336,379 discloses an improvement of a resultant cover. Herein, an isocyanate compound (X) having at least two isocyanate groups in a molecule thereof as a functional group has been dispersed in a thermoplastic resin which is substantially non-reactive with an isocyanate group to obtain an isocyanate mixture. The isocyanate mixture is added to and crosslinked with a thermoplastic polymeric material which is substantially reactive with an isocyanate group to improve the cover.
However, the method which uses a blocked isocyanate as disclosed in Japanese unexamined patent publication No. H11-178,949 has a problem of gasification of a blocking agent which has been disassociated during the molding of the cover. Also, in the method disclosed in Japanese unexamined patent publication No. 2,002-336,379, a crosslinking reaction proceeds during the molding of the cover, since an isocyanate compound dispersed in thermoplastic resin has the reactivity. Thus, the durability of the resultant cover may be lowered in some cases.